The proposed research will investigate the ultrastructural and biochemical roles of subcellular structures in the mechanisms of cell growth. Information now available supports a model for cell growth which includes synthetic and lytic enzymes as well as wall precursors which are deposited in the growing region by exocytosis. This model will be tested by examining the biochemical characteristics of organelles in growing hyphal tips with special attention to apical secretory vesicles and the route of wall precursors through the apical cytoplasm. An integrated ultrastructural-biochemical approach will contribute to a balanced interpretation of new information obtained and an opportunity to increase our understanding of the structural and functional characteristics of growing cells in general.